Hi – thanks for all your replies. Yes I had already seen the information on the motability site that the dealer might charge a cancellation fee. However I also saw information elsewhere which seemed to imply that if you refuse to pay the cancellation fee, there’s not much the dealer could realistically do about it.
He also kind of told us in not so many words that if the order was cancelled, they would probably be able to make more profit on the car by reselling it anyway so they would not have lost anything.